Loads on a system 2

[joesm519]

There is a reducer box whose output shaft drives a conveyor belt. The outrput shaft is off-center (closer to one of the short sides of the rectanglular face of the reducer box). The other end of the reducer box is supported by a vertical rod that is bolted into the ground. I am doing stress analysis of the reducer housing. The weight of the reducer box is the only load I have in my linear static FEA. I did not include the output shaft torque in my FEA since the shaft is free to rotate. My dilemma is that during startup or when the conveyor belt load varies, the reducer box would jerk a little. I am thinking of accounting for these loads (due to the sudden jerk) in dynamic analysis. When the system jerks does any of the torque come into picture in the static stress analysis? I am thinking that the only way the torque will have an effect on the linear static stress analysis is due to friction in the bearing whereby the torque is converted into a load tangent to the output shaft. please let me know if I am on thr right track or missing something.
Thanks

 

[joesm519]

Thank you.

 

[FeX32]

I am glad to see some knowledgeable posts on this tread. I learn something everyday.
I briefly thought about this and I have a little question as well.
EdDanzer/BobM3-
I don't see the bearing supports as reacting the torques. When I picture the moment balance the bearing bores take forces and then correspondingly these forces create the moment you need for equilibrium.
Is this accurate?


Fe

 

[BobM3]

Fe and Joe-

I think you see a freely rotating bearing and assume no torque gets through it into the gear box housing. The way torque is reacted in a gear box is by developing radial loads on offset bearings in the gearbox. Do a simple free-body diagram of a 2 gear mesh. You will develop forces on the teeth of the gears due to the torque. These forces are reacted by radial loads on the bearings. The bearings are offset so the radial loads produce a reacting moment. The result is the gearbox reacts the full input and output torques.

Joe -

The vertical rod as a support is a bit unusual. Usually a gearbox will be bolted to ground through feet that are spread apart. Are you modeling the gear box support correctly?

Also, your problem was a movement of the gearbox on start up and load changes, correct? I don't think a static FEA stress analysis will offer you much insight. My guess is the torque is high during those events and the gearbox is moving because it isn't bolted down sufficiently or the support is moving under the high torque.

 

[FeX32]

Thanks BobM3. Your explanation is precisely what I was thinking.



Fe

 

[EdDanzer]

Torque arm reducers are very common on conveying equipment. These products must be light weight so the frame is flexible making bolted down direct drive gear box a less desirable choice. Chain drives are a poor choice if dirt or dust contamination is present.

When designing the anchor, make it more flexible to help reduce the shock loads during startup. In some of our direct hydraulic motor drives we install a rubber bushing at the anchor to eliminate having the motor flange bolt work loose.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[FeX32]

That's interesting EdDanzer. My first reaction would be to increase the stiffness. Good to know.



Fe

 

[EdDanzer]

Of the many projects that I have optimized with FEA, reducing stiffness in certain areas will reduce stresses in high stress areas without changing deflections much. Some parts may pass stress requirements but fail deflection requirements.

When designing loaded parts and assembled components keep in mind, “Everything is a spring when loaded.”

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com